Effect of oxytetracycline-dosing on the growth, safety and intestinal histology of nile tilapia, Oreochromis niloticus (L.) juveniles

The present study was carried out to evaluate the effect of oxytetracycline (OTC)- dosing at five different concentrations, viz., 0 mg (0X), 80 mg (1X), 240 mg (3X), 400 mg (5X) and 800 mg (10X) kg-1 biomass day-1 for 30 consecutive days on the growth, safety and intestinal histology of Nile tilapia, Oreochromis niloticus (L.) juveniles. The OTC-residues in the edible muscle were detected at scheduled intervals by LCMS/MS. A dose-dependent decline in feed intake, biomass and survival were recorded in OTC-dosed fish. The OTC-residue levels were 0, 204.75±45.75, 318.00±0.00, 778.50±145.50 and 684.00±18.00 ng g-1 in 0X, 1X, 3X, 5X and 10X groups, respectively on day 30 OTC-dosing, which reduced subsequently. Relatively mild histopathological lesions including degeneration of epithelial layer, loss of absorptive vacuoles, necrotized intestinal villi, mucinous degeneration, and necrotized absorptive region were observed in the intestine of OTC-dosed fish. Lamina propria swelling was the characteristic change observed in the 10X group on day 15. The observed data revealed that OTC-dosing is reasonably safe at the therapeutic dose of 80 mg kg-1 biomass day-1 . However, the precise dose for safe usage of OTC is to be determined according to the culture conditions and species cultured.